1. Field of the Invention
The present invention relates to a surface processing method for a mounting stage on which a substrate is mounted, and in particular to a surface processing method for a mounting stage of a substrate processing apparatus that carries out processing on substrates by plasma.
2. Description of the Related Art
Substrate processing apparatuses that carry out plasma processing on wafers as substrates have a housing chamber in which a wafer is housed, and a mounting stage that is disposed in the housing chamber and on which the wafer is mounted. In such substrate processing apparatuses, plasma is produced in the housing chamber, and the wafer is subjected to the plasma processing by the plasma.
The mounting stage is made of aluminum, and a thermally sprayed film made of a ceramic such as alumina is formed on an upper surface of the mounting stage. An electrostatic electrode plate to which a DC voltage is applied is buried in the thermally sprayed film.
When a wafer is mounted on the mounting stage, and a high DC voltage is applied to the electrostatic electrode plate, a potential difference arises between the electrostatic electrode plate and a rear surface of the wafer, so that the wafer is attracted to the mounting stage through a Coulomb force or the like due to the potential difference. That is, the mounting stage acts as an electrostatic chuck.
The mounting stage is disposed on a substantially cylindrical susceptor. The susceptor has therein a coolant chamber and cools the wafer attracted to the mounting stage using a coolant in the coolant chamber during the plasma processing.
The thermally sprayed film on the mounting stage is ground using a grindstone obtained by compacting together abrasive grains and making into a disk shape. However, the surface (mounting surface) of the thermally sprayed film thus ground is still rough when viewed microscopically although it is smooth when viewed macroscopically.
If a number of wafers are subjected to the plasma processing on a wafer-by-wafer basis using the mounting stage having the ground mounting surface, each time a wafer is changed, the wafer and the mounting surface rub against each other, which causes the microscopic roughness of the mounting surface to change. That is, if a number of wafers are subjected to the plasma processing, the mounting surface becomes smooth when viewed microscopically. If the mounting surface becomes smooth, the contact area between a wafer and the mounting surface will increase, thus improving the efficiency of heat transfer from the wafer to the mounting surface, and by extension to the susceptor. As a result, the temperature of a wafer after a number of wafers are subjected to the plasma processing is lower than that of a wafer before a number of wafers are subjected to the plasma processing. Because the plasma processing is affected by the temperatures of wafers, processing results of the plasma processing carried out on a number of wafers cannot be maintained uniform.
Moreover, the present inventors ascertained that changes in the microscopic roughness of the mounting surface caused by the plasma processing saturate when the plasma processing has been carried out on a certain number of wafers (for example, the number of wafers corresponding to about an integrated time period of 3000 hours for which radio frequency electrical power is supplied in normal plasma processing).
To reduce such changes in the microscopic roughness of the mounting surface of the mounting stage, there has been developed a surface processing method for the mounting stage in which the mounting surface is subjected to grinding using a grindstone, lapping using a lapping plate, and lapping using a tape lapping apparatus in this order so that the mounting surface can be made smooth when viewed microscopically (see, for example, Japanese Laid-Open Patent Publication (Kokai) No. 2007-258240).
However, the above described surface processing method requires a number of processing apparatuses (the grindstone, the lapping plate, and the tape lapping apparatus) and a number of steps. For this reason, the above described surface processing method requires much time and effort and thus cannot be readily used. Moreover, the forms in which the grindstone, the lapping plate, and the tape lapping apparatus contact the mounting surface are different from the form in which a wafer contacts the mounting surface. Thus, the mounting surface of the mounting stage to which the above described surface processing method is applied is less likely to conform to wafers.